Wire for an endovascular apparatus

ABSTRACT

An elongate endovascular element for crossing through an obstruction in a blood vessel comprises: a proximal section; a distal tip section of smaller diameter than the proximal section; and a distally-tapering intermediate section extending between the proximal and distal tip sections; wherein the tapered intermediate section has a length that is substantially λ/2 or a multiple of λ/2 , where λ is a wavelength of a driving frequency that will produce longitudinal resonance in the element.

TECHNICAL FIELD

The present invention relates to treatment of ischaemia by using anultrasonically activated wire or other elongate element to cross througha blockage in a blood vessel and to facilitate the introduction offollow-on therapeutic devices.

PRIOR PATENT APPLICATIONS

The invention develops concepts expressed in our International PatentApplication published as WO 2020/094747, and the yet unpublished GBpatent application no. 2006665.0 whose contents are incorporated hereinby reference.

BACKGROUND

In endovascular procedures, an artery is selected and recruited for usein obtaining access to the vasculature. The selection is based on theartery's ability to accommodate the passage of the intended diagnosticor therapeutic device to the target site and the extent to which it mayminimise tissue and patient trauma.

In revascularising procedures, for example in peripheral arteries orveins, access is often made by surgical cutdown and puncture to thefemoral, popliteal, tibial and/or pedal arteries, commonly known inmedical terms as the Seldinger technique. Once the access is made, anintroducer wire and an introducer sheath are inserted into the vesseland secured at the site. This sheath acts as a port for theintroduction, withdrawal and exchange of devices and serves to minimiseabrasion of the arterial tissue. Then guide catheters and guidewires areintroduced into the artery, to provide further protection and to assistdevice navigation and provision of therapy to the target site.

Guidewires are pushed along the lumen of the vessel, carefully to avoidcausing any trauma to the vessel wall, and are navigated to the site ofthe obstruction. In successful procedures, the guidewires are thenpushed across, or through, the obstruction and are kept in situ to actas a guide over which the diagnostic or therapeutic devices, such asballoon catheters and stents, are tracked to the site of the occlusion.Guidewires are used in other minimally-invasive procedures to introduceother devices and instruments into vessels or other cavities of the bodyto enable inspection, diagnosis and different types of treatment.

Guidewires are, for example, used for balloon angioplasty,gastrointestinal, urological, and gynaecological procedures. All suchprocedures require a passageway to be formed through a blockage tofacilitate the passage of larger and often more cumbersome devices tothe site of lesions or other tissues targeted distal to the lesions inthe body.

Guidewires are key to therapeutic intervention and are manufactured fromdifferent materials, most typically stainless steels and various alloys,including NiTi (nitinol), cobalt-chrome (CoCr) etc., with many differentdesigns. Their manufacture often involves the modification of thechemical composition and microstructural morphology of the material, forexample by cold working the material while forming it into a wire andthen machining the wire to different dimensional designs and applyingdifferent thermal treatments to effect a desirable performance. As anexample, specific tapers may be machined over the length of a wire toproduce differential degrees of flexibility along the length of thewire. So, at its distal end, the wire will have sufficient flexibilityto conform to the shape of the vessel, and strength to transmit force tothe tip (‘tip stiffness’) or force to cross through the lesion.

In conventional guidewires, the tapered segments are encased in coils orjacketing materials that allow for flexibility through the tapers whileenabling transmission of force to the distal tip of the wire through thecoils. As will be explained, in wires of the invention, such coils orjacketing materials are not essential as force is transmitted byultrasonic energy to excavate a lumen even if the wire is uncoated orunjacketed.

The length of wires used in endovascular procedures varies depending onthe distance over which they are considered likely to operate. As anexample, wires typically of 750 mm up to 900 mm in length are used inmany peripheral applications where they may be introduced in femoral orpopliteal anatomies, or need to track to and through blockages inipsilateral iliac femoral popliteal and infra popliteal arteries. Wiresthat are used in ipsilateral and coronary applications tend to be of theorder of 1200 mm, 1500 mm or 1700 mm in length. Indeed, wires that maybe tracked contra laterally may be longer, perhaps of the order of 2000mm to 2250 mm or 2500 mm or 3000 mm in length. The most common wirelengths on the market are 1750 mm, 1950 mm and 3000 mm.

In many instances extension wires may be used to facilitate thedeployment of certain therapeutic devices, referred to as over the wire(OTW) devices. In this instance the proximal end of the wire may requirecertain features.

Many conventional endovascular wires are passive mechanical devices withno active components. Passive wires do not transmit any energy otherthan that applied by the clinician. They are operated by their proximalend being pushed, pulled, and torqued to navigate to the blockage siteand are then pushed through or around the blockage. They are of variedconstructions and designs to facilitate access and crossing of lesionsin different anatomies and for different devices. However, in very manyinstances the occlusions are too challenging for conventional wires tocross through. These passive wires then do not work as guidewires areintended to, or they are limited when trying to cross nearly- ortotally-occluded blockages that may also be significantly calcified. Insituations where they are tracked around occlusions, e.g. in asub-intimal situation, such wires are often unsuccessful at re-enteringthe true lumen.

The present invention relates to the use of ultrasonic vibrationstransmitted along wires to cross blockages. Transmission of ultrasonicvibrations along small-diameter catheters and assemblies is disclosed inU.S. Pat. No. 3,433,226. U.S. Pat. No. 5,971,949 describes thetransmission of ultrasonic energy via waveguides of differentconfigurations and tip geometries. U.S. Pat. No. 5,427,118 describes anultrasonic guidewire system but does not discuss in detail proximalgeometries of the wire or how it facilitates follow-on devices viaover-the-wire methods.

Many current single-transducer systems are not ultrasonically activatedguidewires but are instead, ultrasonically activated catheters thatcontain wire members to agitate and ablate material. U.S. Pat. Nos.6,855,123 and 4,979,939 describe such systems. These cathetersthemselves require a separate passive guidewire to help them navigateand, as such, are tools to facilitate a separate guidewire crossing ablockage. U.S. Pat. No. 9,629,643 shows a system with a range of distaltip configurations but all requiring a separate guidewire for access.

These devices are directed towards delivering an alternative method ofrevascularisation and are often described as atherectomy devices,crossing devices or vessel preparation devices. With limited exceptions,they do not identify with crossing through lesions with the purpose ofacting as a device delivery system. In the art, these ultrasonic devicesand recanalisation wire devices enhance revascularisation and providefor, or effect, an atherectomy by de-bulking the lesion by removing theplaque that forms the lesion.

In the early, later and current designs, ultrasonic generator systemsare large because of the acoustics used and they have become largeunits, scaled to generate multiple frequencies and to control the pulsedwave. Also, practical utility considerations mean that known systemscommonly comprise separate elements. For example, many systems aredesigned with the signal generator housed in a separate unit from atransducer, some being mounted on large trolley units, consoles orstands that take up significant space in the clinical environment. U.S.Pat. No. 6,450,975, US 2008/0228111 and U.S. Pat. No. 9,282,984 alldescribe such systems.

Ultrasonically-activated catheter and wire systems have been consideredin the past as a method of crossing or atherectomy and to preparevessels for angioplasty treatment. Some products have been madeavailable commercially in the past, some remain available on the marketand some new systems have come to market recently. Such catheter andwire systems often include an ultrasonic generator and an ultrasonictransducer. The ultrasonic generator converts mains electricity into anultrasonic waveform, defined by its voltage amplitude, current andfrequency. The ultrasonic transducer, and often an amplifying horn,convert the electrical energy into high-frequency mechanical vibrations,defined by frequency and amplitude of vibration.

A small-diameter wire waveguide is coupled at its proximal end directlyto the transducer, or via any horn, and transmits the mechanicalvibrations to the distal tip of the wire. This results in the distal tipof the wire waveguide vibrating at a desired amplitude and frequencywith the goal of excavating material and ultimately facilitating therevascularisation or recanalisation of vessels and anatomical structuresthroughout the body. Tissue and material in the vicinity of the distaltip are affected by a combination of the ultrasonic movement of the tipand its direct mechanical abrasion, ablation and cavitation from thepressure wave components and acoustic streaming that removes ablatedmaterial from the zone around the tip.

In known ultrasonically activated endovascular wire systems, theproximal end of the guide wire is connected to the transducer. In ourpatent application published as WO 2020/094747, the wire runs throughthe transducer and not only extends distally therefrom, but alsoproximally. This allows the user to couple the transducer to the wire atany desired position and to adjust the total length of the distalportion of the wire, without having to cut it. The ability of the wireto travel or extend through the transducer and to be coupled to thetransducer at a plurality of locations has very useful practicalbenefits arising from the ability to adjust the total length of thedistal portion of the wire, for example to adapt to the expected lengthof the trajectory the wire tip needs to travel within the patient'sbody. Also, control of the wire is enhanced in keeping its placement insitu in the vascular lumen whilst adjusting or reconnecting activationsource. Additionally, an adjustable-length distal portion of the wirehelps for achieving and optimising resonance at the distal tip at anydesired frequency.

In developing the concepts disclosed in WO 2020/094747, the inventorshave recognised a need for pre-existing endovascular wires to beimproved in various respects, whether for use with the concepts of WO2020/094747 or otherwise. There is a need for endovascular wires thatcan be manufactured more easily, that can be navigated more easily tothe site of a lesion, that can be activated and controlled more simplyand effectively, and that can cross through the lesion more efficientlywhile forming a larger lumen that is better able to facilitate flowalong a vessel and to accommodate follow-on therapies.

It is an aim of the present invention to address one or moredisadvantages associated with the prior art.

SUMMARY OF THE INVENTION

According to an aspect of the invention there is provided an elongateendovascular element for crossing through an obstruction in a bloodvessel. The element comprises:

-   -   a proximal section;    -   a distal tip section of smaller diameter than the proximal        section; and    -   a distally-tapering intermediate section extending between the        proximal and distal tip sections;    -   wherein the tapered intermediate section has a length that is        substantially λ/2 or a multiple or an even-denominator fraction        of λ/2 in the sequence λ/4, λ/8 . . . , where λ is a wavelength        of a driving frequency that will produce longitudinal resonance        in the element.

The invention also resides in an endovascular apparatus for crossingthrough an obstruction in a blood vessel, the apparatus comprising anelongate endovascular element of the invention and an ultrasonictransducer, mechanically coupled to that element, for ultrasonicallyexciting the distal tip section thereof to facilitate crossing throughthe obstruction.

The invention also provides a method of ultrasonically exciting a distaltip section of an elongate waveguide element, the method comprising:inputting ultrasonic energy into a proximal section of the element at adriving frequency that excites longitudinal resonance in the element;and generating lateral sub-harmonic vibrations in the distal tip sectionin addition to longitudinal vibrations.

The ultrasonic excavating guidewire of the invention differs from otherultrasonic wires and conventional guidewires in various importantaspects.

The invention assists with navigating the wire through the anatomy,crossing through a lesion and opening out a lumen whose diameter isgreater than the diameter of the wire or a bulb or any other enlargedfeature at a distal end of the wire. For this purpose, the distal endportion, which may be tapered or of narrower diameter than a proximalportion of the wire, is left bare to facilitate lateral excavation inthe distal region. In conventional wires and in competing ultrasonicguidewires, the distal end of the wire is tapered down to a narrowdiameter to help the wire to navigate through tortuous anatomies.However, these portions of the wires are sleeved-over with spring-likecoils and or with polymer jackets to enable such flexible elements to bepushed through the anatomy.

The coil or jacket of prior art wires allows for the transmission oflongitudinal load and may have a secondary function of maintaining aconstant diameter over the length of the wire so that follow-ontherapeutic devices that are introduced into the vasculature over theguide wire can do so over a maximum working length. However, in theultrasonic wire of the invention, energy in the form of an ultrasonicdisplacement waveform transmitted through the wire provides a means toenable the wire to pass through obstructions and therefore coils orjackets in the distal end portion of the wire are not essential.

To provide for lateral excavation of occluding materials, the absence ofdistal coils or jackets and the optimisation of the tapered and distalland length and diameter in the invention provide for dual excavation bylongitudinal and lateral displacement of the wire effecting cavitation,abrasion and ablation. The invention allows preferential selection ofsubharmonics in the lateral or radial direction in addition tolongitudinal direction.

To select subharmonic frequencies at the distal end that will excavatein the lateral mode, the distal end portion of the wire is machined inform in accordance with the invention to suit preferential selecteddominant subharmonic resonant frequencies. This maximises lateraldisplacement of the distal end portion through the design of the shapedprofile of the wire with respect to its taper and the length of itsdistal land length and diameter.

For a given material selected for its resilience, toughness andmechanical properties with a characteristic acoustic performance at 37C, the optimal characteristic of the wire in respect to gross length isto be an odd multiple (n=1,3,5, . . . n) of λ/4, where λ is thewavelength in the material for a given input frequency and specificmaterial properties.

The transition of a taper provides a step gain or amplification in theultrasonic energy transmitted distally in the wire. However, theinventors have noted that the natural selection of a dominantsub-harmonic can be effected by making the taper length λ/2. It has alsobeen found that optimal lateral transmission of the wire is obtainedthrough a distal land length of λ.

An important aspect that determines usability is that wires of theinvention have tip flexibility allowing them to conform to the shape ofthe arteries or other vessels that they navigate and to be flexible sothat the lateral mode of oscillation effects a significant forcedisplacement. Thus, wires with a distal land diameter of 0.005″ to0.008″ are preferred, with 0.007″ providing optimal performance in Type1 Nitinol wire with a particular A_(f), e.g. between 5° C. and 18° C.

It is necessary to utilise the excitation-established modes ofdisplacement in the longitudinal and lateral directions without exposingthe wire to elevated levels of stress or strain that could cause thewire to fracture catastrophically. Thus, the wire is mechanicallycoupled to the ultrasonic transducer and is predominantly excited in thelongitudinal direction at a prescribed frequency and amplitude ofdisplacement. The wire geometry is selected to resonate mainly in thelongitudinal mode at or near this input driving frequency, which sets upa standing wave in the wire along its length while in resonance. Thisresults in a significant longitudinal component of vibration in thevicinity of the distal tip.

Another challenge is that whilst the lateral mode of displacement canoccur anywhere along the length of the wire, it is desirable to conveyand to focus energy toward the distal end. In particular, in addition tothe longitudinal mode at or near to the driving frequency of the system,there will be various additional longitudinal sub-harmonics at which awire of a length suitable for anatomical entry will be excited. Further,the wire has lateral or transverse modes of vibration near thelongitudinal primary frequency and its sub-harmonic frequencies. Anyoffset or imbalance introduced in the wire's anisotropy or conformationor geometry will promote these lateral modes of vibration, especially ifthese lateral modes are at or near the longitudinal modes. However, itis desirable to encourage lateral excitation to occur preferentially inthe distal region of the wire.

Lateral displacements occur at frequencies lower than the drive or inputfrequency and their attenuation and amplification of the movement in thewire is dominated by the driving frequency and the geometry andmaterials used in the wire. Such lateral modes are superimposed on thelongitudinal motion of the distal region and in accordance with theinvention may be selected preferentially by incorporating particulardesign features into the wire. Whilst in principle these lateraldisplacements may be present in the wire, the selection of specificfrequencies and modes of vibration can be achieved by tailoring thegeometry of the wire, including the position and length of tapers, andthe magnitude of the movement can be determined by the diameter andmaterial properties of the distal portions of the wire.

There is a need to optimise the wire to get the wire to displace with anoptimal level of force and displacement to excavate a blockage. Thus, inoptimised wires of the invention, the construction of the differenttapers and different lands along the length of the wire can effectdifferent lateral and longitudinal responses in the distal end region ofthe wire. These responses can then be optimised for the different usecases envisioned in different anatomies and with different types oflesions.

There is also a need for guidewires that can quickly navigate to andthrough chronic total occlusions that are composed of hard calcificlesions and to so provide a lumen large enough to allow the passage offollow-on therapeutic devices over the wire. Thus, an objective of theinvention is selectively to excavate occluding materials within a bloodvessel and to open an aperture or lumen substantially greater than thecross-sectional area of the wire to facilitate the delivery of afollow-on therapy. To this end, the mechanisms of excavation in thedistal tip region of the wire comprise direct longitudinal vibrationcoupled to lateral motion that act in unison to ablate and open a lumenin the lesion. This ablation or other excavation mechanisms may occurnot only where the distal tip of the wire contacts the lesion but alsowhere the distal region of the wire contacts the lesion after firstpenetrating the lesion.

Various inter-relating variables can be modified in accordance with theinvention to optimise excavation of a lesion. Specifically, the wiredirects ultrasonic energy from where the wire is coupled to thetransducer to the distal end of the wire. Excavation at this distal tipregion of the wire is determined by the mode (i.e. lateral andlongitudinal movement) and amplitude in which the energy is presented inthe wire and so by: the driving frequency and amplitude driving theultrasonic signal/displacement in the wire through its length; thecharacteristic of acoustic transmission in the wire; and the diametersof the different sections of the wire, namely in a proximal landsection, in an intermediate tapered section and in a distal landsection, affecting amplification and the amplitude of wire displacementin the different regions along the length of the wire as it responds toexcitation.

Thus, the dimensions and uniformity of the wire influence its response,in terms of: the internal composition of the wire and the nature of itsmaterial; the external shape of the wire and any discontinuity or shapedfeature or formation in the wire; the uniformity of the wire in terms ofits shape and dimensions, such as tolerances over length; the taperdimensions, transition sections and their relevance to the appliedultrasonic energy; changes in the diameter of the wire from its proximaldiameter at the transducer to the diameter of its distal excavatingland; the amplification associated with this reduction in diameter overthe length of the wire; and the location and length of the taperedsection and how it corresponds to wavelength.

Selecting the mechanical properties and design of the wire to optimiseits performance recognises that these attributes are relevant to thephysical manifestation of transverse or lateral motion.

All of these objectives of the invention have to be achieved with a wirethat is also flexible enough to confirm to the shape of the anatomythrough which it passes in use. In particular, the flexibility andelasticity or resilience of the wire determines whether the wire can fitwithin the lumen of an artery or other vessel. The diameter andmechanical strength of the wire also determines whether the wire cantrack through, or navigate through, tortuous anatomy and so follow theshape of the vessel and not jam, stall or, worse, penetrate the wall ofthe vessel, due to being unable to deflect and to adopt the shape of theanatomy. In this respect, in the case of femoral arteries the vesselsare large and so the ability of the wire to conform to their shape isless challenging than, for example, in the pedal arteries, whosetortuosity is similar to that of coronary arteries and some of thelarger neurovascular anatomies.

Collectively, wire design parameters can be selected to control how muchenergy is coupled into the longitudinal modes and lateral modes. Inpreferred embodiments, the ratio of the diameter of the proximal segmentdefining the working length of the wire to the diameter of the distalsegment defining the excavating section of the wire is between 2:1 and3:1, which offers an optimal gain or amplification.

The optimal length of the tapered section to select the a dominantsecondary frequency is λ/2, i.e. the ratio of the length of the taperedsection to the length of the distal land length is λ/2:A with theeffective length of the wire from the coupling to the distal tip beingan odd multiple of λ/4 ((2n+1) λ/4).

A wire is an example of an elongate endovascular element of theinvention that may be used as a waveguide or wave delivery system. Forexample, the element could be a hybrid of a wire and a catheter. Inparticular, a proximal portion of the element, for example about thefirst metre of the element from the proximal end, could have a wireencapsulated in a manner akin to a catheter whereas a distal portion ofthe element extending to the distal end could be an unencapsulated wire.A wire or other element of the invention could be the inner component ofan overall wave delivery system.

The design of the transmission member or waveguide wire is optimised tocontrol the transmission of the wave pattern through different anatomiesto the distal tip and through different materials. The morphology of thematerials used is critical and whilst they can, at a ‘macroscopic’level, present as an isotropic material morphology that is highlyresilient, they can have anisotropic micromorphological features thatcan either delay the onset of a starter crack or inhibit the progressionof a crack.

The materials used in the embodiments are extensively cold-workedstainless steels, nickel titanium alloys and/or cobalt/chromium alloys,e.g. linear elastic nitinol.

Specifically, in the case of the NiTi only alloys, tight control isexercised over the inclusion size and population in order to limit thelikelihood of fracture. In other alloys, control is exercised over othermorphological features that may act to promote premature failure of thewire.

The invention allows for the introduction of specific features that aremachined into the wire at the proximal and the distal end and over itslength to enhance its ability to cross through the lesion, to strengthenthe wire, to enable greater control over the wire, to enable coupling ofthe wire and efficient transmission through the wire. The composition ofthe designs varies with materials used and the intended use.

The geometry of the wire as well as the materials used are optimised fordifferent application use cases. The wires are machined to minimizedefects and to optimise the transmission through tightly controlledtapers and keying splines over the length and through sections of thelength of the material.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of examplewith reference to the accompanying drawings, in which:

FIG. 1 is a schematic perspective view of an ultrasonic wire systemaccording to the invention.

FIG. 2 is a perspective view of a hand-held ultrasonic activation unitand a wire with locating markings.

FIG. 3 is a schematic side view of a wire in accordance with theinvention.

FIG. 4 is an enlarged side view of a distal end portion of a wire inaccordance with the invention.

FIG. 5 is an enlarged view of a distal end portion of a wire in avariant of the invention.

FIGS. 6 and 6 a are side views of a wire of the invention, showing itsresponse to excitation.

FIG. 7 is a schematic side view of an active wire having anangularly-offset distal end portion.

FIGS. 8a and 8b are schematic side views of a further active wire of theinvention, including marker bands.

FIG. 9 is a schematic side view of another active wire of the invention.

FIGS. 10 and 11 are schematic side views of other active wires of theinvention, each having an enlarged, bulbous distal tip

FIG. 12 is a side view of a wire of the invention, showing an effect ofjacketing the wire.

FIGS. 13a, 13b, and 13c are schematic perspective views, showing endportions of a wires in variants of the invention.

FIGS. 14a, 14b, and 14c are schematic perspective views, showing endportions of a wires in further variants of the invention.

DETAILED DESCRIPTION

FIG. 1 of the drawings shows the overall configuration of a systemaccording to the invention and illustrates some major components of sucha system. This example features a handheld ultrasonic activation unit 2through which a flexible transmission member in the form of anendovascular wire 4 extends, in central alignment.

The wire 4 can be inserted into a patient's vasculature and traversed tobring its distal end to the location of a lesion. Once a complex lesionis encountered that resists the wire 4 crossing it, the activation unit2 can be coupled to the wire 4 at a suitable longitudinal location. Whenactivated, the activation unit 2 transmits ultrasonic vibrations to andalong the wire 4, enhancing the ability of the wire 4 to cross thelesion through ablation and other mechanisms. The wire 4 thereby servesas a crossing wire for crossing through an occlusion in a blood vesseland can then remain in situ to serve as a guide wire for deliveringsubsequent therapeutic devices to treat the lesion.

Typically, the wire 4 may, for example, be more than 2 m and up to 3 min length. For example, access to a lesion in or through the foot mayinvolve the wire travelling a distance of typically 1200 mm to 2000 mmwithin the vasculature depending on whether an ipsilateral,contralateral or radial approach is chosen. In this respect, a wire 4tapering distally to a fine wire at its tip can navigate to the pedalarteries and around the pedal arch between the dorsal and plantararteries. However, the invention is not limited to pedal or otherperipheral applications and could, for example, be used in coronaryapplications, where the ability of the wire 4 to navigate to and toexcavate within tortuous small-diameter arteries is also beneficial.

The diameter of the distal section of the wire 4 will determine theflexibility of the wire 4 and its ability easily to conform to the shapeof the anatomy through which it is intended to pass. Thus, for example,in a tortuous (pedal or coronary) anatomy, a distal section of adiameter of 0.005″ to 0.007″ combines flexibility with the ability toexcavate occlusive material.

The activation unit 2 includes user controls 6 and optionally also adisplay. The activation unit 2 further comprises a distal hand toggle 8that a user can turn about the central longitudinal axis of the unit 2and of the wire 4. In particular, the activation unit 2 can slide overthe wire 4 and can be coupled to the wire 4 at a plurality oflongitudinally spaced locations by applying torque to turn the toggle 8.To effect coupling, the toggle 8 acts on a coupling such as a colletwithin the activation unit 2 that surrounds and is coaxial with the wire4. When the toggle 8 is tightened, the collet grips the wire 4 totransmit ultrasonic energy from an integrated ultrasonic transducerwithin the activation unit 2, optionally via an amplifier horn that iscoupled to the transducer. The wire 4 could be coupled directly to thetransducer in some embodiments, in which case the horn may be omitted.

The toggle 8 is reversible to release the activation unit 2 from thewire 4. Provision is thereby made to interchange wires 4 of differentdimensions, configurations, or materials for different purposes. Thereis also the possibility of interchanging the transducer or the hornwithin the activation unit 2.

FIG. 1 shows a disaggregated arrangement in which an ultrasonic signalgenerator 10 is separate from the activation unit 2. In this example,the ultrasonic signal generator 10 is connected to the activation unit 2by a connector cable 12. In alternative arrangements the ultrasonicsignal generator 10 may be incorporated into the housing of theactivation unit 2. The example shown in FIG. 1 has an externally poweredultrasonic signal generator 10 and therefore comprises a power cable 14that connects to an external source of electrical power. Alternativeembodiments may be powered by internal batteries, which can, e.g., beincorporated into the ultrasonic signal generator unit 10 or into theactivation unit 2.

In general, the components of the system are preferably portable and aremore preferably hand-held. The components may be wireless, rechargeable,reusable, and recyclable. Any external cable 12, 14 for conveying poweror signals may be coupled through a slip ring to allow free rotation ofthe cable 12, 14 and to avoid entanglement with the wire 4 or it mayprovide a conduit for the proximal portion of the wire 4.

A semi-automated control system can control or modulate the signal fromthe generator 10 applied to the transducer and horn of the activationunit 2 and hence to the crossing wire 4 based on feedback from thewire-tissue interaction in order to control the signal being transmittedto adjust for losses due to damping or increased resistance ormodulating applied force. Visual and haptic feedback indicators canoffer visual, audio and/or tactile feedback to the user regarding thestatus of the device, the nature of the tissue being ablated andindicate the level of force that can be applied to effect ablation anddisruption of the tissue and progression of the crossing wire.

The system may contain a means to provide a manual override to assistcontrol of the amplitude of vibration delivered to the distal tip. Thisallows the system to be controlled by the user operating the device inthe course of the procedure, through controllers and user inputmechanisms located on the generator and transmission unit or to becontrolled autonomously.

As will be explained, the distal end of the wire 4 is suitably alsooptimised for tracking through anatomies under ultrasound imaging modes,as well as having marker bands to highlight position under x-ray. It mayhave radio-opaque markers to indicate the working length and thecrossing tip of the wire.

FIG. 2 shows how the wire 4 may be etched or otherwise marked with aseries of optimum zonal markings 92 to guide the user in choosinglengths of the wire 4 that encourage distal activation. The user canthen align the coupling of the activation unit 2 with the zonal markings92 on the wire 4, optionally using other markings appropriately locatedon the housing 18 of the activation unit 2. This approach applies toboth straight-through embodiments in which a proximal portion of thewire 4 emerges from the housing 18 of the activation unit 2 axially andother embodiments in which a proximal portion of the wire 4 emergeslaterally at a position along the length of the housing 18.

The markings 92 address a challenge in the control of the system, namelythe manner in which ultrasonic energy is coupled to the wire and theimportance at locating the point of connection at specific regions thatwill couple best. The markings 92 placed on the proximal segment of thewire 4 ensure that this alignment is clear to the physician. Thesemarkings 92 also facilitate the physician reconnecting the activationunit 2 to the wire 4 at different locations during a procedure.

To address visibility and alignment for excitation, the markings 92 maybe aligned with a reference point on the activation unit 2, for examplea reference point on a strain relief feature at the distal end of thehousing 18 to denote the best point of location. Visualisation of themarkings 92 may be improved by adding illumination and/or a transparentor translucent window to the activation unit 2, for example positionedon a distal strain relief feature of the unit 2.

The markings 92 are apt to be applied by laser etch beading or othermeans, such as the application of a coating and/or a jacket, to mark thesurface of the wire 4 in a way that allows the user to discriminate thebest points of connection along the length of the wire 4. It isconsidered that modifying the oxide surface layer or the finish of thewire 4 is the best way to achieve this. The period or longitudinalspacing of these markings will be λ/2 and their length will be afunction of the efficiency of coupling energy into the wire 4, which isalso a function of its mechanical and dimensional properties.

In an example of the invention, the markings 92 on the wire 4 couldindicate any of a plurality of lengths where the distal section of thewire 4 emerging from the housing 18 of the activation unit is at or neara resonant length and the proximal section is not at a resonant length.In other words, attachment zone markers 92 are positioned optimally onthe wire 4 such that, when coupled to the acoustic source, the length ofthe distal portion from the coupling point to the distal tip is equal toa resonant length whereas the length of the proximal portion from thecoupling point to the proximal tip is equal to a non-resonant length. Inpractice, these markings 92 may be located at positions tailored to thesystem to take into account bends and other design features that mayaffect the resonant response.

When using ultrasonic energy to excite the wire 4, it is desirable tooptimise displacement amplitude in the distal tip portion of the wire toexcavate a lesion. Conversely, it is desirable to minimise displacementor movement of the proximal end of the wire, which is outside thepatient's body and indeed may hang freely from the proximal side of theactivation unit 2.

To achieve this, the distal length of the wire 4 from the distal tip towhere the activation unit 2 is coupled to the wire 4 should be an oddmultiple of a quarter wavelength of the ultrasonic wave. This creates astanding wave in the wire with a vibrating antinode at the distal tip,hence maximising the amplitude of vibration at the distal tip.

Consequently, locating the distal end of the transducer at odd multiplesof the quarter wavelength from the distal tip of the wire 4 willmaximise vibration at the distal tip. Conversely, ensuring that thelength of the proximal section is a multiple of half the wavelength fromthe transducer fixation will minimise vibration at the proximal end ofthe wire 4.

When coupled to the ultrasonic transducer 20 in the activation unit 2, awire 4 of the invention undergoes axial ultrasonic vibration and can beconsidered as a fixed-free rod under longitudinal or axial vibration.The natural frequencies of a fixed-free rod under longitudinal or axialvibration are given by the expression:

${\omega_{n} = {\left( \frac{{2n} - 1}{2} \right)\frac{\pi c}{L}}},{n = 1},2,3,\ldots$

where c=the speed of sound in the wire material;

-   -   L is the length of the rod; and    -   ω=natural frequency of the system=2πf

The ultrasonic activation unit 2 applies a constant known frequency andthe speed of sound c of the wire 4 can be experimentally measured orapproximated by the expression:

$c = \sqrt{\frac{E}{\rho}}$

where E=Youngs Modulus of the wire material; and

-   -   ρ=density of the wire material

For a system that applies a constant or near-constant frequency, thewire 4 lengths, L, at which resonance will occur are given by:

${L = {\frac{{2\pi} - 1}{4}\lambda}},{n = 1},2,3,\ldots$

Indeed, in a through-wire system, from the point of connection of thewire 4 to the transducer, the wire 4 can be considered as two fixed-freerods undergoing longitudinal axial vibration. One rod extends distallyand the other rod extends proximally from the activation unit 2.

As an example, a particular nitinol alloy has a speed of sound ofapproximately 3400 m/s. For a drive frequency of 40 kHz, the wavelengthλ can be calculated to be approximately 85 mm. Resonant lengths cantherefore be determined and marked at optimum positions on the wire 4.The wavelength further impacts on the selection of taper locations andtaper lengths along the wire 4.

FIGS. 3 to 7 show various preferred and optional features of the wire 4.

In general, the wire 4 has features to allow it to integrate with thehandheld activation unit 2. For example, location markers are providedto guide optimal positioning and attachment of the activation unit 2 tofacilitate attachment and release at a plurality of longitudinallocations. Thus, over a significant length of its proximal section, aseries of optimum attachment locations are etched or otherwise marked onthe wire 4 to guide the user in locating and selecting the optimumattachment locations for distal ultrasonic transmission from theactivation unit 2. The housing 18 of the activation unit 2 can also havea marker that can be aligned with the wire 4 marking prior to coupling.

As with all endovascular wires, a balance between flexibility or‘trackability’ and rigidity or ‘pushability’ is required. However,unlike passive wires, the wire must be able to transmit ultrasonicenergy to the distal region in order to assist in crossing lesions. Inthis way, the wire 4 functions as an excavator, not just at its tip butalso along part of its length. The wire 4 has a distal land length thatacts radially as a lateral excavation device for opening an aperture.The wire may have distal shaped lengths to amplify radial excavation.

The wire 4 includes regions where the geometry tapers to affect a changein diameter, either from a larger to a smaller diameter or from asmaller diameter to a larger diameter. In regions where tapers arerequired and at other locations, sections may be welded or otherwisejoined together end to end. Such welds or joins must be able towithstand the stresses arising from transmission of ultrasonic energy inaddition to normal modes of bending and cyclic fatigue. Alternatively,the entire wire 4 or parts of the wire 4 could be ground or similarlyprocessed to achieve the desired geometry.

The wire 4 may therefore be fabricated from sections welded togetherend-to-end. For example, a proximal section may be machined as astandard diameter to provide for amplification as well as to provide astandard connection for a proximally-loaded activation unit 2. Theproximal section can be welded to one of a selection of differentdiameter wires that may have custom distal ends and tips. Thus, sectionsmay be chosen and combined in various ways. This beneficially reducesthe requirement to hold stock of various wire diameters as sections of afew different wire diameters may be assembled to produce wires 4 of manyrequired configurations. Welding the proximal segment to the distalsegment facilitates more efficient manufacturing and more efficienttransmission if post-processing is performed on the wire, and allowswelding of different materials to a proximal NiTi base if desired.

Ideally, tapers can be chosen to begin at lengths equal or nearly equalto multiples of the half wavelength of the wire system. This places thestart of the tapers at anti-nodes of a standing wave in the wire 4,where the amplitude of vibration is at a maximum. Preferably, thelengths of the tapered sections are chosen to be equal or nearly equalto half wavelengths of the resonant system. In general, welds or joinsshould be located at longitudinal positions where the stress is at aminimum. As the welds or joins are at locations of low stress, the loadsapplied to them in the course of activation of the wire will not lead tocatastrophic fatigue failure.

The wire 4 shown in FIG. 3 comprises a proximal section 124, a centralor intermediate section 128 and a distal excavating section 130 forcrossing a lesion. The intermediate section 128 is narrower than theproximal section 124 but is wider than the distal section 130. Theintermediate section 128 is therefore joined to the proximal section 124by a tapering proximal transition 132 and to the distal section by atapering distal transition 134. Each section is welded to the next by aweld 122 on the proximal side of the respective transitions.

The proximal section 124 has a series of longitudinally spaced zonalmarkings 92 like those in FIG. 2 to guide the user in choosing wirelengths that encourage distal activation and that discourage proximalactivation. The wire 4 further comprises radio opaque marker bands 136to aid tracking of the intermediate 128 and distal sections 130 within apatient's anatomy during the procedure. These various markers 136 areapt to be created by plasma vapour deposition, atomic layer depositionor sputtering, for example of sputtered gold, to resist ultrasonicloading.

The proximal section 124, the intermediate section 128 and the distalsection 130 are all generally straight and in mutual alignment along acentral longitudinal axis of the wire, albeit substantially flexible tobe bent along their length. However, a compound distal end portion 138of the wire 4 has a shape set to be bent away from the general axis ofthe wire 4 in the remainder of the distal section 130. These bends orheat set shapes enhance lateral motion in addition to longitudinalmotion of the wire 4.

Specifically, as also shown in FIG. 4, the distal end portion 138comprises an inboard angled leg 140 and an outboard distal tip 126 atthe distal end of the angled leg 140. The leg 140 is inclined relativeto the general axis of the wire 4 and the distal tip 126 is inclinedrelative to the angled leg 140. The distal tip 126 may be a bulbous orotherwise enlarged feature as 25 shown in FIG. 4 and a coating 142 mayextend part-way along the length of the angled leg 140, leaving thedistal extremity of the angle leg 140 and the distal tip 126 uncoated.

In this example, the distal tip 126 is inclined further than the angledleg 140 away from the general axis of the wire 4. Thus, the distal tip126 and the angled leg 140 are both inclined in broadly the samedirection away from the general axis of the wire 4. In other examples,however, the inclination of the distal tip 126 is closer than the angledleg 140 to the general axis of the wire 4. Potentially, the distal tip126 could even be approximately parallel to the general axis of the wire4 in the remainder of the distal section 130.

To recap, the total length of the distal portion of the wire 4 from thedistal tip 126 to the connection point or coupling of the activationunit 2 may be equal to the resonant length for the wire 4. Ideally thetaper length is equal to a multiple of half the wavelength. Thediameters of the various sections of the wire 4 are chosen for anoptimal balance between pushability and trackability, in addition tobeing able to allow follow-on devices of standard dimensions to use thewire 4 as a guidewire.

In this example, the wire 4 includes angled parts positioned atlocations to enhance steerability of the wire 4 when tracking to thelocation of a lesion. By way of example, the angled leg 140 may be 15 mmto 25 mm in length and the distal tip 126 may be 2 mm to 5 mm in length.The angled leg 140 facilitates steering through the anatomy whereas thedistal tip 126 facilitates tracking through small-diameter lesions. Theangle between the angled leg and the remainder of the distal section 130is typically 10° to 40°. This angle provides a means to navigate intobranches but is not so great as to promote stresses that exceed thefatigue limit of the wire 4. The angle between the distal tip 126 andthe angled leg 140 is typically 10° to 30°. This enables navigation indiseased small-diameter vessels.

The wire 4 may be heat-treated, for example by annealing after machiningand shaping the tip 126, to optimise its microstructure to resistfatigue.

Visibility of the wire 4 under x-ray or other imaging mode may beenhanced with the addition of radiopaque marker bands or coatings 136chosen to optimize visibility under well-established imaging modes. Thewire 4 may also have coatings 142, such as hydrophilic coatings, toreduce friction with surrounding catheters or tissue.

FIG. 5 shows that the wire 4 may have a distal coil or polymer jacket144 attached or bonded over the distal section 130. The jacket shownhere terminates distally just before a bend in the wire 4 thatfacilitates deflection of the distal tip 126. The distal tip 126 of thewire 4 may be coated or processed to harden the surface or increase itsablative properties.

FIGS. 6 and 6 a show a wire 4 that has a substantially straight proximalsection or land 124, a distally-tapering intermediate section 130 and asubstantially straight excavating part or land providing a distal tipportion 126 for crossing a lesion. By virtue of the taper of theintermediate section 130 between them, the distal tip portion 126 has asmaller diameter than the proximal section 124. For example, theproximal section 124 may have a diameter of 0.43 mm and the distal tipportion 126 may have a diameter of 0.18 mm or 0.25 mm. The taper in theintermediate section 130 is slight and so is greatly exaggerated inthese drawings. The tapering intermediate section 130 may extend over amultiple of λ in length or a fraction of A in length, that fractionpreferably having with a numerator of 1 and an even denominator—forexample in the sequence ½, ¼, ⅛ . . . —whereas the distal tip portion126 may have a length of λ/2 or a multiple of λ/2 or a fraction of λ/2such as λ/4.

The overall geometry of the wire 4 including its nominal diameter andlength and the driving frequency of the system are determined by thecharacteristic speed of sound in the material of the wire. Thischaracteristic is a function of that material's properties and itsgeometry. The dimensions of the straight and tapered sections of thewire are machined at functional intervals of wavelength.

As an example of nitinol with a Young's Modulus of approximately 75 GPa,λ, λ/2 and λ/4 are determined to be 84 mm, 42 mm and 21 mm in thisexample. The chosen frequency will produce harmonics along the length ofthe wire and the loading of the tip of the wire will assist inestablishing standing waves for non-characteristic lesions. The distalsection 126 can be tapered or can be uniform in diameter along itslength. The system may produce lateral and longitudinal displacementsover a range of frequencies away from that of the drive frequency, oftenoccurring at sub-harmonics of the frequency in the distal section 126.

As an example, which does not preclude other dimensional values, a wirewith a core cross section diameter of 0.43 mm has a tapered section 130optimally located to transition to a distal wire diameter to 0.18 mm.The lengths of each section of the wire can be chosen to have alongitudinal resonant mode at or near the driving frequency, such as 40kHz, with strong sub-harmonics at or near 20 kHz, 10 kHz or others.Through appropriate design, there are neighbouring lateral modes near 40khz and 20 khz or others. There may be amplification across the taper bya factor of approximately 2.4 or other suitable value. As the wireemerges from a catheter or sheath, additional lower-frequency lateralvibrations may be induced through a cantilever action.

As a result, through appropriate selection of wire material, geometryand distal design features, desirable lateral modes will be energisedeven when the wire is driven with longitudinal vibrations. In unison,both the longitudinal and lateral vibrations contribute to excavation ofthe lesion and result in the wire opening an aperture or lumen in thelesion whose internal diameter is substantially greater than the wirediameter.

In terms of length, the overall length of the wire may be a function ofan odd multiple of λ/4. The active length, being the distance from theproximal connection point to the distal tip of the wire, may also be afunction of an odd multiple of λ/4.

The purpose of the tapered transition 130 is to provide gain and tosustain the transmission of energy through the wire. The tapered sectionwill also affect how a lateral mode of displacement may be establishedin the distal land section 126 of the wire.

The point at which the taper is introduced may also assist withfacilitating a change of materials between one part of the wire andanother, which could create a differential in wavelength between thedistal and proximal segments.

Tapered transitions may vary in diameter in a stepped, exponential,radial or linear manner. For the purpose of amplification, the change inthe cross-sectional area represents a level of gain in both lateral andlongitudinal displacement amplitudes in the wire. The length and thediameter of the distal section 126 will determine the mode and magnitudeof displacement in axial and radial directions.

As the goal of the activated wire 4 is to cross and excavate a lesion,its dimensions are optimised with the purpose of excavating as large anaperture as possible at a given input. In this respect, FIG. 6 showsthat the distal section 126 of the wire 4, once activated, moves in aprimary longitudinal mode, moving in and out, and also in a radialdirection which maps out and excavates a greater volume at the distalend through the longitudinal movement of the wire 4. The distal section126 of the wire 4 is also seen to move through lateral and undulatingmovements at or near the drive frequency and secondary modes ofdifferential harmonics, dependent on the activating frequency and alsothe length of the distal section 126. These wave forms may interferewith each other and be more or less effective in excavating material atdifferent moments.

FIG. 6 further shows how the distal end section 126 of the wire 4 mayexcavate an aperture whose diameter is greater than the diameter of thewire and so create a larger lumen through which therapies may beintroduced to a lesion. In this example, again, a catheter sleeve or apolymer jacket 144 terminates before an unjacketed distal section 130 ofthe wire. The distal section 126 of the wire 4, once activated, moves ina primary longitudinal mode, moving in and out, and also in a radialdirection which maps out and excavates a greater volume at the distalend through the longitudinal movement of the wire 4. The distal section126 of the wire 4 is also seen to move in other modes through lateraland undulating movements under the resonant wave 146 and secondary modesof differential harmonics, dependent on the activating frequency, thelength of the distal section and the tortuosity of the anatomy.

Thus, when activated with ultrasonic energy, the wire 4 acts as anexcavation tool for excavating material distal to the distal tip of thewire 4 by virtue of longitudinal movement and then through the offsettranslation or lateral motion of the wire 4 within the vasculature whichprovides a lateral offset. Thus, the wire 4 abrades the inner surface ofthe occlusion not just at its distal tip but also along some of itslength extending proximally from the distal tip and so forms a wideraperture for the passage of follow-up therapeutic devices over the wire4. As the wire 4 extends beyond the distal end of the lesion, thelateral displacement continues to excavate within the body of the lesionand so forms a larger lumen.

FIG. 7 shows a wire 4 that is formed or shaped to have anangularly-offset distal excavating section for crossing a lesion. Inthis embodiment, the distal section is not straight but is angled byvirtue of a heat-set shaped tip 126. The dimensions of the tip 126 areoptimised to provide improved performance in terms of steering to alesion and excavation of the lesion. In particular, the angle of the tip126 relative to the longitudinal axis of the distal section and thelength of the tip 126 determine the ability of the wire 4 to turn into aspecific side-branch vessel. The angle and the length of the tip 126also affect the manner in which the wire 4, once activated, willexcavate a section of stenosed material If the dimensions of the tip 126are characteristic of a harmonic, e.g. λ/8 or about 11 mm in length, thewire 4 will open out a significantly larger tunnel in a lesion than saya 25 mm tip section. The amplitude of the waveform and the number oftimes the distal section of the wire 4 is passed through a calcificsection will determine the diameter of the tunnel that is excavated.

The wire 4 may not necessarily be shaped or angled at its tip but whereit is shaped or angled at its tip, the angle is chosen carefully. If theangle of the tip 126 is too great, it will create a larger lever arm andso could fatigue the wire 4 excessively; conversely if the angle of thetip 126 is too small, then the wire 4 may not be steerable effectively.In this respect, FIG. 7 shows that the tip 126 may be offset from thelongitudinal axis of the wire 4 by about 15° to 45°, allowing the tip126 to disrupt and excavate a greater volume of a lesion. The tip 126 issuitably heat-treated, for example at over 500° C. for less than 10minutes, in order to create a microstructure that is reliably resistantto crack propagation and hence to fatigue.

FIGS. 8a and 8b show how visibility of the location of the wire 4 in thepatient's body may be enhanced by the use of marker bands 194, forexample of gold. Such marker bands 194 may, for example, be fixed atlocations close to (for example, about 3 mm from) the distal tip 126 ofthe wire 4 and also from the distal end of the proximal section 184,just before the start of the tapered intermediate section 186. Themarker bands 194 are placed at locations of minimal load in use of thewire 4. This minimises the possibility that the marker bands 194 couldbecome detached or that the wire 4 could fail at those locations. Themarker bands 194 are apt to be flush-fitted into circumferential groovesthat are ground around the wire 4.

FIG. 9 shows a variant in which the distal tip 126 of the wire 4 isrounded, with no sharp transitions. By way of example, in this instancethe proximal section 184 may be 1800 mm long, the tapered intermediatesection 186 may be 84 mm long and the distal section 188 may be 10 mmlong. Again, marker bands 194 encircle the wire 4 close to the distaltip 126 of the wire 4 and the distal end of the proximal section 184.

FIGS. 10 and 11 show other variants of the wire 4 that each have abulbous distal tip 198, which is rounded to avoid sharp transitions butcould instead be chamfered or faceted, preferably with obtuse anglesbetween facets, with distally-converging facets that ease passage of thewire through the anatomy. Enlargements such as bulbs may be located atthe distal tip and/or be spaced slightly from the distal tip, and couldcover a radiopaque coil or other materials.

The bulbous tip 198 may, for example, be 3 mm to 4 mm in length and mayhave a diameter of just over 0.4 mm, or from 0.010″ to 0.035″ forexample. Apart from its bulbous tip 198, the wire shown in FIG. 10 isotherwise analogous to the wire 4 shown in FIG. 9. Again, the wires 4shown in FIGS. 10 and 11 have circumferential marker bands 194 that maybe flush-fitted into circumferential grooves ground around the wire 4.Conveniently, as shown, the bulbous tip 198 may be encircled by one ofthe marker bands 194.

In the example shown in FIG. 11, the wire has a proximal portion thatcomprises a straight section 200 and a distally tapering section 202.The straight section 200 may have a ridged or otherwise textured surfaceas shown, to improve engagement with an activation device. The proximalportion is welded to an intermediate portion that constitutes most ofthe length of the wire 4. The intermediate portion also comprises astraight section 204 and a short distally tapering section 206. A markerband 194 is shown encircling the straight section 204 close to thedistally tapering section 206 of the intermediate portion 194. Finally,a short, narrow distal section 208 extends distally from theintermediate portion 186 to the bulbous tip 198.

FIG. 12 illustrates how jacketing or thickly coating the wire, forexample with a polymer jacket or coil 144, leaves a desired distallength clear or unjacketed and free to oscillate laterally as shown. Theeffect of jacketing or coating could also be emulated by a catheteraround the wire 4. The distal extent of jacketing has been found tocontrol the aperture created by the distal excavating section 130 of thewire 4. The wire 4 excavates a lesion up to the collar or edge 148 atthe distal end of the jacket 144. It has been found that if theunjacketed distal length of the wire is not sufficiently long, anaperture of not much more than the diameter of the wire may be createdin a lesion, inhibiting even the progression of the wire through ablockage.

In particular, jacketing the wire 4 below or beyond a resonant orharmonic length, so that the distal edge 148 of the jacket 144 does notcoincide with a resonant or harmonic length, hinders formation of anaperture. Conversely, jacketing the wire 4 up to a resonant or harmoniclength, so that the distal edge 148 of the jacket 144 substantiallycoincides with a resonant or harmonic length, allows the wire 4 toexcavate a larger aperture.

FIGS. 13a, 13b, and 13c show a selection of arrangements of the distaltip 126. FIG. 13a shows the wire 4 encircled by a radio-opaque band 136and provided with a rounded bull tip 150, for example of beryllium. FIG.13b shows a radio-opaque coil 151 welded around the distal tip section126 of the wire 4. FIG. 13c shows an oversized beryllium tip 152 toincrease effectiveness when crossing long calcific sections. The distaltip section 126 may be heat-treated to increase its fatigue resistance.

FIGS. 14a, 14b, 14c show other arrangements of the distal tip 126. FIG.14a shows a looped tip 154 with an outer surface that is coated orotherwise modified to optimize drilling or excavation over the looprather than being confined to a tip. The loop may also aid navigation tothe site of a blockage. FIG. 14b shows a diamond-coated tipped burr 156.FIG. 14c shows a drilling end tip 158 or segment that is coated with adiamond and/or carbide coating. Coatings and hardened materials such asthese provide for aggressive machining of lesions.

In general, wires 4 of the invention are apt to be made of superelasticalloys, such as nitinol (nickel-titanium), which are known to havepreferential properties in the transmission of ultrasound whileproviding a balance of flexibility and pushability. Linear elasticnitinol arising from advances in processing alloys of nickel andtitanium may also be used for wires of the invention, as can betatitanium. Surface finishes and coatings applied to the wires 4 mayinclude resilient fluoropolymers and hydrophilic coatings to reducefriction.

Many other variations are possible within the inventive concept. Forexample, a coating may be provided along a discrete segment of the wire,such as by coating a mid-section of the length of the wire to leavedistal and proximal end portions of the wire uncoated for excavation andfor clamping an activation unit, respectively. Continuous and brokensegments of coating along the length of the wire may allow for selectiveclamping and unclamping of an activation unit at desired positions.

PTFE or alternative polymeric jackets may be employed to reduce frictionand risk of damage to the interior of a guide catheter

Polymer jackets may be employed in a distal section for improvedradiopacity, more generally along the wire to provide for lubricity, orto provide a marking point to connect to a transducer of an activationunit.

Surface modification may involve addition of striations or serrationsinto the surface of the distal end portion to bite further into calcificlesions so as to assist excavation and resist damage. Such formationsmay be directional so to take advantage of the direction of motion andto amplify the efficiency of cutting or abrasion of the occludingmaterial. Nevertheless, individual formations may have a smooth ratherthan sharp contours so as not to damage the vessel wall. Similarly,materials may be applied to the wire to create an additional abradingsurface to assist in excavating material. Such materials may usefullyreduce the area of the wire that is in contact with the lesion topromote cutting and to prevent calcified material blocking vibration andmovement of the wire.

Drawn filled tubing (DFT) may be employed, in which a NiTi core issurrounded by a second metal that has different properties, for examplestainless steel. As the relative thickness of that secondary layer canbe controlled, it could be used to create marker bands for coupling orshaping of the wire, or for promoting lateral damping.

A jacket of a shaped alloy could provide for navigation and/or opacity.The use of a more ductile compliant outer jacket could avoid coldworking of nitinol and the need for post-process thermal treatment.

Potentially, there could be multiple cutting planes defined by multiplelands at a distal tip or end region of a wire. This could facilitatedifferent and potentially more anatomically-suited distal end gain aswell as a second proximal land of possibly greater diameter to betterwork on the lesion. This is one way of creating multiple lateralexcavation zones, others being different section diameters, differenttapers and different excavation land profiles.

It is noted that the many features of the various embodiments describedabove are not limited to those specific embodiments only. A skilledperson will be able to combine features from one embodiment withfeatures of other embodiments wherever this is technically possible andmakes sense from a practical point of view.

1. An elongate endovascular element for crossing through an obstructionin a blood vessel, the element comprising: a proximal section; a distaltip section of smaller diameter than the proximal section; and adistally-tapering intermediate section extending between the proximaland distal tip sections; wherein the tapered intermediate section has alength that is substantially λ/2 or a multiple or an even-denominatorfraction of λ/2 in the sequence λ/4, λ/8 . . . , where λ is a wavelengthof a driving frequency that will produce longitudinal resonance in theelement, and wherein the proximal section of the element is marked witha series of longitudinally-spaced location markers, spaced apart fromeach other by a distance of substantially λ/2, to guide the user incoupling an activation unit for optimal activation of the distal tipsection.
 2. The element of claim 1, wherein the location markers areapplied to the element by modifying a surface layer or finish of theelement or by applying a coating or a jacket to the element.
 3. Theelement of claim 1, wherein the distal tip section has a length that issubstantially λ/2 or a multiple of λ/2, where λ is a wavelength of adriving frequency that will produce longitudinal resonance in theelement.
 4. The element of claim 3, wherein the distal tip section has alength of substantially λ.
 5. The element of claim 1, wherein the distaltip section has a diameter of between ⅛ and ½ that of the proximalsection.
 6. The element of claim 1, wherein the proximal section has adiameter of from 0.014″ to 0.035″ (about 0.36 mm to about 0.89 mm). 7.The element of claim 1, wherein the distal tip section has a diameter offrom 0.003″ to 0.014″ (about 0.08 mm to about 0.36 mm).
 8. The elementof claim 7, wherein the distal tip section has a diameter of 0.005″ to0.008″.
 9. The element of claim 8, whose distal tip section has adiameter of substantially 0.007″.
 10. The element of claim 1, having anoverall length that is a function or multiple of (2n+1) λ/4, where λ isa wavelength of a driving frequency that will produce longitudinalresonance in the element.
 11. The element of claim 1, wherein theproximal section has a length of λ/4 +nλ/2, where λ is a wavelength of adriving frequency that will produce longitudinal resonance in theelement.
 12. The element of claim 1, wherein the proximal section has alength being an odd multiple of λ/4, where λ is a wavelength of adriving frequency that will produce longitudinal resonance in theelement.
 13. The element of claim 1, comprising at least one welded joinbetween at least two of said sections.
 14. The element of claim 1,wherein the distal tip section comprises a bulbous or otherwise enlargedfeature at a distal extremity.
 15. The element of claim 1, wherein thedistal tip section comprises a distal portion that is offset angularlywith respect to a longitudinal axis of the wire.
 16. The element ofclaim 1, wherein a marker band encircles at least the distal tipsection.
 17. The element of claim 1, having an overall length of between500 mm and 3000 mm.
 18. The element of claim 1, wherein the proximalsection is of substantially uniform diameter along its length.
 19. Theelement of claim 1, wherein the proximal section has a length of from500 mm to 2900 mm.
 20. The element of claim 1, wherein the distalsection is tapered or of a constant diameter along its length.
 21. Theelement of claim 1, wherein the length of each of said sections is afunction or multiple of λ/4, where λ is a wavelength of a drivingfrequency that results in longitudinal resonance in the wire.
 22. Theelement of claim 1, further comprising marker bands positioned on thedistal tip portion and near a distal end of the proximal section. 23.The element of claim 1, wherein the distal tip portion is partiallyjacketed or coated or partially covered by a catheter, leaving a lengthof the element extending to its distal tip unjacketed or uncoated. 24.The element of claim 23, wherein the jacket, coating or catheter extendsto a resonant or harmonic length of the element.
 25. The element ofclaim 1, wherein a mid-section of the length of the element is jacketedor coated and at least part of the proximal section is unjacketed oruncoated.
 26. The element of claim 25, wherein the proximal section hasdiscontinuous, longitudinally interrupted jacketing or coating.
 27. Theelement of claim 1, wherein at least a distal portion of the distal tipsection comprises a bare wire, not jacketed or coated.
 28. Anendovascular apparatus for crossing through an obstruction in a bloodvessel, the apparatus comprising an elongate endovascular element ofclaim 1 and an ultrasonic transducer, mechanically coupled to thatelement, for ultrasonically exciting the distal tip section thereof tofacilitate crossing through the obstruction.
 29. The apparatus of claim28, comprising a coupling between the element and the transducer andbeing configured to input the ultrasonic energy into the element at adriving frequency whose wavelength is λ.
 30. The apparatus of claim 29,wherein the coupling is positioned substantially at an odd multiple ofλ/4 from a distal tip of the element.
 31. The apparatus of claim 29,wherein the coupling is positioned substantially at a distance of (2n+1)λ/4 from a distal tip of the element.
 32. The apparatus of claim 29,wherein a proximal portion of the wire extending proximally from thecoupling has a length being, substantially, a multiple of λ/2.
 33. Theapparatus of claim 29, wherein each of the sections has a lengthselected to have a longitudinal resonant mode at or near the drivingfrequency with first and second sub-harmonics at or near ½ and ¼ of thedriving frequency, respectively.
 34. The apparatus of claim 29, whereinthe activation unit comprises at least one visualisation feature being areference point for alignment with the location markers or illuminationand/or a window for visualising the location markers. 35-41. (canceled)